Fig. 4

Site-to-reference spectral ratio as a function of distance for ambient vibration Survey A (for location, see Fig. 1). The black line shows the frequency band, which comprises the values 2–4 Hz. Seismic sensors are marked as black squares. Station 1 is situated at zero distance, and has Swiss coordinates 635,442.012/126,064.684. Shown are: a fault-normal component; b fault-parallel component (i.e. horizontal, perpendicular to fault-normal); c vertical component. Clearly visible is a decay of spectral ratio between station 5 and 9 in the normal and parallel component, and between stations 5 and 10 in the vertical component, and a subsequent recovery of spectral ratio in all three components, which marks the change of physical properties along the profile. In all three components, a spectral ratio minimum could be measured along a length of about 40 m